Isoflavones (soybean isoflavones: daidzein, genistein, glycitein) contained in soybeans have structures similar to estradiol, and have anti-estrogen actions associated with binding to estrogen receptors (hereinafter referred to as ER) and estrogen-like actions. The epidemiological studies and intervention studies of soybean isoflavones that have been done before suggest their preventive effects due to their anti-estrogen actions on breast cancer, prostate cancer and other hormone-dependent cancers and improving effects due to estrogen-like actions on menopausal disorders, postmenopausal osteoporosis and hyperlipidemia.
Recently, it has been pointed out that the active principle of the physiological effects of these soybean isoflavones may be a metabolite of daidzein, equol. More specifically, it has been reported that equol has an ability to bind to ER (especially to ERβ) greater than soybean isoflavones and that it has remarkably high transition capability to target organs such as breast and prostate tissues. Moreover, a case-control study reports that there are significantly less patients who produce equol in the patients of breast cancer and prostate cancer. The effects of soybean isoflavones to improve the bone density and lipid metabolism were examined regarding postmenopausal women categorized into two groups: those who produce equol and those who do not. A significant improvement in those who produce equol was observed.
Equol is produced by metabolism of daidzein by enteric bacteria. The abilities to produce equol vary between individuals, and the percentage of Japanese who produce equol production is reportedly about 50%. That is, about 50% of Japanese are not able to produce equol (non-equol-producing individuals). Such an individual cannot enjoy useful physiological benefits based on the action of equol even if they ingest soybeans and processed soybean foods. Therefore, in order to attain useful physiological benefits based on the action of equol in a non-equol-producing individual, ingesting equol itself is thought to be effective.
A known method of producing equol is subjecting a raw material containing daidzein compounds to fermentation treatment by microorganisms (hereinafter referred to as equol-producing bacteria) which metabolize daidzein to produce equol. Known starting materials containing daidzein for use in this production method include soybeans, Ge Gen Tang (Chinese traditional medicine, also known as Kakkonto), red globe grapes, alfalfa or others. Moreover, equol-producing bacteria are already known. For example, bacteroides E-23-15 (FERN BP-6435), streptococcus E-23-17 (FERN BP-6436), streptococcus A6G225 (FERN BP-6437) and lactococcus 20-92 (FERN BP-10036) have been isolated from human excrement by the inventors of the present invention (refer to patent documents 1 and 2).
However, simply subjecting the above-mentioned starting materials containing daidzein compounds to fermentation treatment by using equol-producing bacteria cannot yield sufficient amount of equol in the fermented product, and there has been the problem that desired useful benefits based on the action of equol cannot be sufficiently expected by ingesting the fermented product as it is.
In contrast, the hypocotyl portions of soybeans have been known to contain isoflavones, saponins and other useful components in a proportion higher than in the cotyledon portions which are used as processed soybean foods, and various uses have been developed for its extract (e.g., patent document 3). However, soybean hypocotyl extract itself is disadvantageously expensive. Moreover, when the soybean hypocotyl extract is used as a starting material for producing equol, addition of other nutrients are necessary to allow fermentation by equol-producing bacteria, which can be another problem. For these reasons, the soybean hypocotyl extract cannot be currently used as a starting material for industrially producing equol.
Meanwhile, since the soybean hypocotyl itself has a characteristic bitterness, there is a trend to avoid using the substance itself as it is, and much of the soybean hypocotyl is currently disposed. Furthermore, likewise soybean cotyledon portions, soybean hypocotyls contain allergens, therefore the soybean hypocotyl could not be taken by or administer to people suffering from soybean allergy. Therefore, to effectively utilize the soybean hypocotyl itself, it is important to impart added values to increase its usefulness.    [Patent document 1] International Publication WO99/007392    [Patent document 2] International Publication WO2005/000042    [Patent document 3] Japanese Unexamined Patent Publication No. 2002-234844